Various prior art systems are available using magnetic tape, a magnetic or optical disk, and an optical tape for the storage and retrieval of information. Each of these systems have certain objectives. For example, magnetic tape or magnetic disk is typically used for the storage and retrieval of information on computers and the like. However, an increasing number of users of stored information are facing requirements of expanded storage capacity, faster and better retrieval, and lower cost than found in for example, the prior art magnetic tape or magnetic disk data storage systems. Therefore, there has been a move to denser and denser magnetic disks and tapes, and, more recently, to optical disks and optical tapes.
U.S. Pat. No. 4,661,941 (A. Bell et al.), issued on Apr. 28, 1987, and U.S. Pat. No. 4,669,070 (A. Bell), issued on May 26, 1987, disclose an optical tape record and playback system. More particularly, in a recording process, a laser has its coherent light beam modulated by data to be recorded. The laser transmits this coherent non-circular light beam into a collecting objective lens which images the beam onto a beam expander that changes the non-circular light beam into a circular light beam. The circular light beam is then transmitted through a polarizing beam splitter and quarter-wave plate and onto a switching mirror which switches back and forth. The beam reflected by the switching mirror is reflected by a series of mirrors and onto the optical tape. In a playback mode the laser is biased to emit a linearly polarized continuous light beam with a predetermined intensity that does not disturb the absorptive layer of the optical tape. The light beam takes the same path to the optical tape used to record information thereon, but the polarization is changed by the quarter-wave plate. The light reflected from the optical tape returns over the same path to the quarter-wave plate where the polarization is again changed in order that the light beam is reflected by the polarization beam splitter onto a photodetector. The light pattern of the reflected light beam is converted into representative electrical signals by the photodetector for use by a data using device.
U.S. Pat. No. 5,081,617 (D. Gelbart), issued on Jan. 14, 1992, discloses an optical system for reading and tracking multiple tracks of optically recorded data. For reading optically stored data, polarized light from a laser diode is collected by a collecting lens and is then shaped by a shaping lens into a narrow line of light. The light in the line of light is polarized parallel to the length of the line and is reflected by a polarizing beam splitter through a quarter-wave plate where the polarization in the line of light is changed to a circular polarization. The line of light impinges across a plurality of recorded tracks on the optical tape. The reflected light beam is transmitted back through the quarter-wave plate where the polarization is changed to a linear polarization normal to the original laser light beam. Such polarized light beam is directed straight through the polarizing beam splitter and imaged onto a light detector array via and imaging lens.
It is desirable to provide a simple and inexpensive digital optical tape read system which provides improved resolution of an image of a recorded data pattern stored on an optical tape at a detector array from resolutions obtained in prior art optical tape system of similar, or even greater complexity.